[1] Simulated future summers (i.e., 2049-2051) and annual (i.e., 2050) average regional O 3 and PM 2.5 concentrations over the United States are compared with historic (i.e., [2000][2001][2002] summers and all of 2001) levels to investigate the potential impacts of global climate change and emissions on regional air quality. Meteorological inputs to the CMAQ chemical transport model are developed by downscaling the GISS Global Climate Model simulations using an MM5-based regional climate model. Future-year emissions for North America are developed by growing the U.S. EPA CAIR inventory, Mexican and Canadian emissions and by using the IMAGE model with the IPCC A1B emissions scenario that is also used in projecting future climate. Reductions of more than 50% in NO X and SO 2 emissions are forecast. Impacts of global climate change alone on regional air quality are small compared to impacts from emission control-related reductions, although increases in pollutant concentrations due to stagnation and other factors are found. The combined effect of climate change and emission reductions lead to a 20% decrease (regionally varying from À11% to À28%) in the mean summer maximum daily 8-hour ozone levels (M8hO 3 ) over the United States. Mean annual PM 2.5 concentrations are estimated to be 23% lower (varies from À9% to À32%). Major reductions in sulfate, nitrate and ammonium PM 2.5 components combined with the limited reduction in organic carbon suggests that organic carbon will be the dominant component of PM 2.5 mass in the future. Regionally, the eastern United States benefits more than the rest of the regions from reductions in both M8hO 3 and PM 2.5 , because of both spatial variations in the meteorological and emissions changes. Reduction in the higher M8hO 3 concentrations is also estimated for all subregions and fewer days with M8hO 3 above the air quality standards in urban sites with Atlanta in the southeast benefiting most.Citation: Tagaris, E., K. Manomaiphiboon, K.-J. Liao, L. R. Leung, J.-H. Woo, S. He, P. Amar, and A. G. Russell (2007), Impacts of global climate change and emissions on regional ozone and fine particulate matter concentrations over the United States, J. Geophys.

Extensive research has improved our understanding and forecast of the occurrence, evolution and global impacts of the El Niño–Southern Oscillation (ENSO). However, ENSO changes as the global climate warms up and it exhibits different characteristics and climate impacts in the twenty-first century from the twentieth century. Climate models project that ENSO will also change in the warming future and have not reached an agreement about the flavor, as to the intensity and the frequency, of future ENSO conditions. This article presents the conventional view of ENSO properties, dynamics and teleconnections, and reviews the emerging understanding of the diversity and associated climate impacts of ENSO. It also reviews the results from investigations into the possible changes in ENSO under the future global-warming scenarios.

Abstract. Aerosol impacts on NO 2 photolysis rates and ozone production in the troposphere are studied by applying a modem sensitivity analysis technique "ADIFOR" on a coupled transport/chemistry/radiative transfer model. Four representative types of tropospheric aerosol (rural, urban, maritime, and desert) are evaluated in terms of loading strength and radiative characteristics. The effects of relative humidity (Rid), aerosol vertical loading profile, and NOx (NO+NO2) emission are also studied. The presence of absorbing aerosols in the boundary layer is found to inhibit near-ground ozone formation and to reduce ground level ozone by up to 70% in polluted environments. The presence of strongly scattering aerosols may increase ozone concentration in the lower boundary layer, but their effects vary with season, NOx, nonmethane hydrocarbon emission (NMHC), and temperature. Ozone production in the upper troposphere can be either enhanced or weakened, depending on the scattering and absorbing ability of aerosol particles and availability of NOx. In the lower troposphere, NO 2 photolysis and ozone production rates are most sensitive to urban aerosol, followed by rural, then desert, and finally, maritime aerosol. As expected, NMHC, and NOx emissions also are found to have a large influence on O3 formation.

westerlies due to the weakening of the southeastern portion of the Atlantic subtropical high. These effects of the TP heating explain a remarkable portion of the effects by the Asian continent heating. In addition, the impacts of different magnitudes of TP surface heating are also discussed.

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The role of emissions of volatile organic compounds and nitric oxide from biogenic sources is becoming increasingly important in regulatory air quality modeling as levels of anthropogenic emissions continue to decrease and stricter health-based air quality standards are being adopted. However, considerable uncertainties still exist in the current estimation methodologies for biogenic emissions. The impact of these uncertainties on ozone and fine particulate matter (PM 2.5 ) levels for the eastern United States was studied, focusing on biogenic emissions estimates from two commonly used biogenic emission models, the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Biogenic Emissions Inventory System (BEIS). Photochemical grid modeling simulations were performed for two scenarios: one reflecting present day conditions and the other reflecting a hypothetical future year with reductions in emissions of anthropogenic oxides of nitrogen (NO x ). For ozone, the use of MEGAN emissions resulted in a higher ozone response to hypothetical anthropogenic NO x emission reductions compared with BEIS. Applying the current U.S. Environmental Protection Agency guidance on regulatory air quality modeling in conjunction with typical maximum ozone concentrations, the differences in estimated future year ozone design values (DVF) stemming from differences in biogenic emissions estimates were on the order of 4 parts per billion (ppb), corresponding to approximately 5% of the daily maximum 8-hr ozone National Ambient Air Quality Standard (NAAQS) of 75 ppb. For PM 2.5 , the differences were 0.1-0.25 g/m 3 in the summer total organic mass component of DVFs, corresponding to approximately 1-2% of the value of the annual PM 2.5 NAAQS of 15 g/m 3 . Spatial variations in the ozone and PM 2.5 differences also reveal that the impacts of different biogenic emission estimates on ozone and PM 2.5 levels are dependent on ambient levels of anthropogenic emissions.

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Impact of climate change alone and in combination with currently planned emission control strategies are investigated to quantify effectiveness in decreasing regional ozone and PM2.5 over the continental U.S. using MM5, SMOKE, and CMAQ with DDM-3D. Sensitivities of ozone and PM2.5 formation to precursor emissions are found to change only slightly in response to climate change. In many cases, mass per ton sensitivities to NO(x) and SO2 controls are predicted to be greater in the future due to both the lower emissions as well as climate, suggesting that current control strategies based on reducing such emissions will continue to be effective in decreasing ground-level ozone and PM2.5 concentrations. SO2 emission controls are predicted to be most beneficial for decreasing summertime PM2.5 levels, whereas controls of NO(x) emissions are effective in winter. Spatial distributions of sensitivities are also found to be only slightly affected assuming no changes in land-use. Contributions of biogenic VOC emissions to PM2.5 formation are simulated to be more important in the future because of higher temperatures, higher biogenic emissions, and lower anthropogenic NO(x) and SO2 emissions.